In an ashram perched high on a hill above the noisy city of Guwahati in north-east India is a small exhibit commemorating the life of India's most famous son. Alongside an uncomfortable-looking divan where Mahatma Gandhi once slept is a display reminding visitors of something the man himself said in 1921: "Of all the evils for which man has made himself responsible, none is so degrading, so shocking or so brutal as his abuse of the better half of humanity; the female sex (not the weaker sex)."

One evening two weeks ago, just a few miles downhill, a young student left a bar and was set upon by a gang of at least 18 men. They dragged her into the road by her hair, tried to rip off her clothes and smiled at the cameras that filmed it all. It was around 9.30pm on one of Guwahati's busiest streets – a chaotic three-lane thoroughfare soundtracked by constantly beeping horns and chugging tuk-tuks. But for at least 20 minutes, no one called the police. They easily could have. Many of those present had phones: they were using them to film the scene as the men yanked up the girl's vest and tugged at her bra and groped her breasts as she begged for help from passing cars. We know this because a cameraman from the local TV channel was there too, capturing the attack for his viewers' enjoyment. The woman was abused for 45 minutes before the police arrived.

Within half an hour, clips were broadcast on Assam's NewsLive channel. Watching across town, Sheetal Sharma and Bitopi Dutta were horrified. "I was fuming like anything. There was this horrible, brutal assault being shown on screen – and the most disturbing thing was, the blame was being put on the woman, who, the report emphasised, was drunk," says Sharma, a 29-year-old feminist activist from the North-East Network, a women's rights organisation in Guwahati. "The way it was filmed, the camera was panning up and down her body, focusing on her breasts, her thighs," says Dutta, her 22-year-old colleague.

When the police eventually turned up, they took away the woman, who is 20 or 21 (oddly, Guwahati police claimed not to know exactly). While NewsLive re-played pixellated footage of her attack throughout the night, she was questioned and given a medical examination. No attempt was made to arrest the men whose faces could clearly be seen laughing and jeering on camera. Soon afterwards, the editor-in-chief of NewsLive (who has since resigned) remarked on Twitter that "prostitutes form a major chunk of girls who visit bars and night clubs".

It was only a few days later, when the clip had gone viral and had been picked up by the national channels in Delhi, that the police were shamed into action. By then, Guwahati residents had taken matters into their own hands, producing an enormous banner that they strung up alongside one of the city's arterial roads featuring screen grabs of the main suspects. Six days after the attack, the chief minister of Assam, the state where Guwahati is located, ordered the police to arrest a dozen key suspects. He met the victim and promised her 50,000 rupees (£580) compensation.

The damage was already irreversible. Most Indians know full well how tough life as a woman can be in the world's biggest democracy, even 46 years after Indira Gandhi made history as the country's first female prime minister in 1966. But here, caught on camera, was proof. And in Assam – a state long romanticised as the most female-friendly corner of the country, largely thanks to the matrilineal Khasi tribe in Meghalaya. The nation was outraged.

"We have a woman president, we've had a woman prime minister. Yet in 2012, one of the greatest tragedies in our country is that women are on their own when it comes to their own safety," said a female newsreader on NDTV. She went on to outline another incident in India last week: a group of village elders in Baghpat, Uttar Pradesh, central India, who banned women from carrying mobile phones, choosing their own husbands or leaving the house unaccompanied or with their heads uncovered. "The story is the same," said the news anchor. "No respect for women. No respect for our culture. And as far as the law is concerned: who cares?"

There is currently no special law in India against sexual assault or harassment, and only vaginal penetration by a penis counts as rape. Those who molested the woman in Guwahati would be booked for "insulting or outraging the modesty of a woman" or "intruding upon her privacy". The maximum punishment is a year's imprisonment, or a fine, or both.

As a columnist in the national Hindustan Times said of the attack: "This is a story of a dangerous decline in Indians and India itself, of not just failing morality but disintegrating public governance when it comes to women." Samar Halarnkar added: "Men abuse women in every society, but few males do it with as much impunity, violence and regularity as the Indian male."

Halarnkar then offered as proof a survey that caused indignation in India last month: a poll of 370 gender specialists around the world that voted India the worst place to be a woman out of all the G20 countries. It stung – especially as Saudi Arabia was at the second-worst. But the experts were resolute in their choice. "In India, women and girls continue to be sold as chattels, married off as young as 10, burned alive as a result of dowry-related disputes and young girls exploited and abused as domestic slave labour," said Gulshun Rehman, health programme development adviser at Save the Children UK, who was one of those polled.

Women travelling on a bus in Chennai, southern India. Photograph: Gustafsson/Rex Features

Look at some statistics and suddenly the survey isn't so surprising. Sure, India might not be the worst place to be a woman on the planet – its rape record isn't nearly as bad as the Democratic Republic of the Congo, for instance, where more than 400,000 women are raped each year, and female genital mutilation is not widespread, as it is in Somalia. But 45% of Indian girls are married before the age of 18, according to the International Centre for Research on Women (2010); 56,000 maternal deaths were recorded in 2010 (UN Population Fund) and research from Unicef in 2012 found that 52% of adolescent girls (and 57% of adolescent boys) think it is justifiable for a man to beat his wife. Plus crimes against women are on the increase: according to the National Crime Records Bureau in India, there was a 7.1% hike in recorded crimes against women between 2010 and 2011 (when there were 228,650 in total). The biggest leap was in cases under the "dowry prohibition act" (up 27.7%), of kidnapping and abduction (up 19.4% year on year) and rape (up 9.2%).

In June, a father beheaded his 20-year-old daughter with a sword in a village in Rajasthan, western India, parading her bleeding head around as a warning to other young women who might fall in love with a lower-caste boy.

But the story that outraged most women in India last week was an interview given to the Indian Express by Mamta Sharma, chairwoman of the National Commission of Women (NCW), a government body tasked with protecting and promoting the interests of Indian women. Asked by the reporter if there should be a dress code for women "to ensure their safety", Sharma allegedly replied: "After 64 years of freedom, it is not right to give blanket directions ... and say don't wear this or don't wear that. Be comfortable, but at the same time, be careful about how you dress ... Aping the west blindly is eroding our culture and causing such crimes to happen."

She added: "Westernisation has afflicted our cities the worst. There are no values left. In places like Delhi there is no culture of giving up seats for women. It is unfortunate that while the west is learning from our culture, we are giving ourselves up completely to western ways."

Her remarks caused a storm. As Sagarika Ghose put it in the online magazine First Post: "It's not just about blindly aping the west, Ms Sharma. It's also about the vacuum in the law, lack of security at leisure spots, lack of gender justice, lack of fear of the law, police and judicial apathy and the complete lack of awareness that men and women have the right to enjoy exactly the same kind of leisure activities."

The Guardian asked Sharma for an interview to clarify her remarks but our requests were ignored.

Maini Mahanta, the editor of the Assamese women's magazine Nandini ("Daughter"), believes the NCW chair's remarks are indicative of what she calls the "Taliban-plus" mentality that is creeping into Indian society. "In this part of the world, it's worse than the Taliban," she insists in her Guwahati office. "At least the Taliban are open about what they like and dislike. Here, society is so hypocritical. We worship female goddesses and yet fail to protect women from these crimes and then blame them too."

Indian women, such as these three in Bawana, on the outskirts of Delhi, frequently come under pressure to abort female foetuses. Photograph: Gethin Chamberlain

Mahanta explains how traditions still cast women as helpless victims rather than free-thinking individuals in control of their own destiny. Girls still tie Raksha bandhan or "safety ties" around their brothers' wrists as a symbol of their duty to protect them, she says. She complains, too, about the Manu Sanghita, an ancient Indian book that she claims preaches: "When a girl is young, she is guided by her father; when she is older, she is guided by her husband; when she is very old, she is guided by her son." She despairs of the cult of the "good girl, who is taught to walk slowly 'like an elephant' and not laugh too loud".

Sheetal Sharma and Bitopi Dutta, the young feminists from the North East Network, complain that modern women are divided into "bad" and "good" according to what they wear, whether they go out after dark and whether they drink alcohol. "We are seeing a rise of moral policing, which blames those women who are not seen as being 'good'," says Sharma. "So if they are abused in a pub, for example, it's OK – they have to learn their lesson," adds Dutta, 22, who grumbles that young women such as herself cannot now hold hands with a boyfriend in a Guwahati park, let alone kiss, without getting into trouble with the moral police, if not the real police.

Many women agree the response from the Guwahati authorities shows they are blind to the root cause: a society that does not truly respect women. Instead, a knee-jerk reaction was taken to force all bars and off-licences to shut by 9.30pm. Club Mint, the bar outside which the young woman was molested, had its licence revoked. Parents were urged to keep a close eye on their daughters.

Zabeen Ahmed, the 50-year-old librarian at Cotton College in Guwahati, tells how she was out for an evening walk not long ago when she was stopped by the police. "They asked me what I was doing out at that at that time – it was 10.30pm or so – and they asked me where my husband was."

The fact that India has a female president – Pratibha Patil – and Sonia Gandhi in control of the ruling Congress party means very little, insists Monisha Behal, "chairperson" of the North East Network. "In the UK, you have had Margaret Thatcher – if you are being harassed by a hoodlum in the street there, do ask: 'How can this be when we have had a woman prime minister?'" she says.

Every Indian woman the Guardian spoke to for this article agreed that harassment was part of their everyday lives. Mahanta revealed that she always carries chilli powder in her handbag if she ever has to take public transport and needed to throw it in the face of anyone with wandering hands. Deepika Patar, 24, a journalist at the Seven Sisters newspaper in Assam, says city buses were notorious for gropers. "If women are standing up because there are no seats, men often press up against them, or touch their breasts or bottom," she explains.

In June, an anonymous Delhi woman wrote a powerful blog post detailing what happened when she dared not to travel in the "ladies carriage" of Delhi's modern metro. After asking a man not to stand too close to her, things turned nasty. Another man intervened and told the first to back off, but soon the two were having a bloody fight in the train carriage. Rather than break up the brawl, the other passengers turned on the woman, shouting: "This is all your fault. You started this fight. This is all because you came into this coach!" and "You women always do this. You started this fight!" and "Why are you even here? Go to the women's coach."

Speaking under condition of anonymity, the 35-year-old blogger says she had experienced sexual harassment "tonnes of times". "I hate to use the word, but I'm afraid it has become 'normal'," she says. "Like if you're in a lift, men will press up against you or grab you or make a comment about your appearance. It's because of this that I stopped travelling by buses and started travelling by auto rickshaws, and eventually got a car myself – to avoid this ordeal. When the metro was launched I loved it – it's an improvement in public transport, very well maintained, you feel safe. Then this happened and I was blamed."

By Thursday last week, the Guwahati molestation case had become even murkier. Police had arrested and charged 12 men with "outraging the public decency of a woman", and on Friday they charged journalist Gaurav Jyoti Neog of NewsLive with instigating the attack he filmed. Neog denies orchestrating the attack or taking any part in it, apart from filming it "so that the perpetrators can be nabbed". But police have forced him to give a voice sample, which has been sent to a forensic laboratory for analysis, to compare with the footage. The verdict is out on that case, but one thing is clear: 91 years after Gandhi urged Indian men to treat their women with respect, the lesson has yet to be learned.

• This article was amended on 24 July 2012. The original said brothers tied Raksha Bandhan threads around their sisters' wrists, when it is the sisters who put the threads on the wrists of their brothers.